1. Field of the Invention
The invention is based on a turn-off circuit for a circuit having at least one self-commutated electrical valve according to the preamble of claim 1.
2. Discussion of Background
The preamble of the invention refers to a prior art which is known from EP-B1-0 161 738. In this specification, a common turn-off device is specified which is connected in parallel with the inverter of a converter on the direct-current side. To turn-off the inverter, the load current is commutated to the turn-off circuit. This applies a counter voltage to the inverter which turns off the current to the inverter. The turn-off circuit exhibits a series circuit of a diode and a turn-off capacitor. A ring-around reactor is connected in series with a thyristor in a parallel branch to the turn-off capacitor. A diode is connected in antiparallel with this thyristor.
In this common turn-off device, the hold-off interval or minimum turn-off period of the inverter thyristors is permanently set by the ring-around period of the common turn-off device, that is to say by the magnitude of the inductance of the ring-around reactor.